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ASTR/GEOL-2040: Search for life in the Universe: Lecture 26

ASTR/GEOL-2040: Search for life in the Universe: Lecture 26. Europa Water & Cracks Life in Lake Vostok. Axel Brandenburg (Office hours: Mondays 2:30 – 3:30 in X590 and Wednesdays 11-12 in D230). Conversion of units: 2 examples. Standard unit for density: kg/m 3

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ASTR/GEOL-2040: Search for life in the Universe: Lecture 26

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  1. ASTR/GEOL-2040: Search for life in the Universe: Lecture 26 • Europa • Water & Cracks • Life in Lake Vostok Axel Brandenburg (Office hours: Mondays 2:30 – 3:30 in X590 and Wednesdays 11-12 in D230)

  2. Conversion of units: 2 examples • Standard unit for density: kg/m3 • Example 1: length in km, e.g.1012 kg/km3 = ?? • Example 2: length in cm, mass in g 1g/cc =

  3. Io 3.57 g/cc Europa 2.97 g/cc Ganymede 1.94 g/cc Callisto 1.86 g/cc Galilean moons: why this change in r?

  4. Outer moons less dense? • Accreted less material • Accreted lighter material • Suffered less heating • Outer moons are larger • Larger orbits

  5. Orbital Resonance Io Europa Ganymede Callisto Tidal Heating

  6. Outer moons less dense? • Accreted less material • Accreted lighter material • Suffered less heating • Outer moons are larger • Larger orbits

  7. Why tidal heating? • Because of tidal locking • Close proximity to Jupiter • Orbit is elliptical • Water bulges

  8. Why tidal heating? • Because of tidal locking • Close proximity to Jupiter • Orbit is elliptical • Water bulges

  9. Io 3.57 g/cc Europa 2.97 g/cc Ganymede 1.94 g/cc Callisto 1.86 g/cc Galilean moons: why this change in r?

  10. Comparison • 3400 rem …

  11. Europa: interior Warm ice..or..liquid water? or some combination?

  12. Ocean in Europa? • Europa has no magnetic field of its own • Galileo probe saw: induced magnetic field • Time-varying magnetic field from Jupiter • 11 hours period • Continuous conducting layer • Brine (salty) ocean • Range of values of conductivity

  13. California’s San Andreas Fault Europa Astypalaea Linea San Andreas Fault

  14. Icebergs? (25 miles across)

  15. Tilted ice blocks look like the Arctic Ocean too…

  16. Tyremulti-ring impact structure Few large impact craters: -> Suggests 60 Myr surface age. A couple of multi-ringed impacts: -> Penetrated 20 km thick ice!

  17. Europa: ocean and atmosphere • surface pressure of Europa's atmosphere is 10−12 atm • tenuous ionosphere • H2, O2, O that escapes Europa's gravity form a gas torus in the vicinity of Europa's orbit around Jupiter -> feeds Jupiter’s magnetospheric plasma • A lot of water • periodically occurring plumes of water 200 km high

  18. Plumes on EuropaHubble Space Telescope

  19. Europa: potential habitability • one of the top locations in the Solar System in terms of potential habitability and the possibility of hosting life

  20. Future Europa missions • ~ 2022 Europa Clipper, 50m res imaging • ~ 2027 Europa Lander • Hydrobots for the future

  21. Robotic submarine • Melt + gravity • Self-sterilizing techniques • Testing of hydrobots in Lake Vostok

  22. NASA’s Valkyrie cryobot • First tests in 2014 in ManatuskaGlacier • Planned testing for Lake Voskok • Developed in 1960s to study glaciers • Lake Vostok discovered later (1973)

  23. Liquid water in Lake Vostok? • Because of high pressure • Because of insulation by the ice • Because of geothermal heat • Because of salt content • Because of tidal force

  24. Liquid water in Lake Vostok? • Because of high pressure • Because of insulation by the ice • Because of geothermal heat • Because of salt content • Because of tidal force

  25. Why liquid water? • Pressure helps (but very little) • Insulation from the top is important • Important: geothermal heat: 50 mW/m2 • basal melting 1mm/yr • 125 m / (1mm/yr) = 125,000 yr • Lake is freshwater: no salts • Tides detected in lake, but unimportant for melting

  26. Earth’s structure • cc

  27. Gondwana Antarctica • Supercontinent 0.6 – 0.16 Gyr • Gondwana split 160 Myr ago (0.16 Gyr) • Antarctica still tropical 55 Myr • 35 Myr cooler • Snow  ice

  28. Lake Vostok on Antarctica • Lake 50 km size • Existed the whole time • Possibility of ancient lake sediments • Unique record of life & climate • Became sealed off 15 Myr ago • Suggestion: constant supply of freshly molten water  frozen ice carried away

  29. Lake Vostok • Ice cores: age > 420,000 yr • Halted 100m above lake: to avoid contamination • Kerosene, Freon (anti-freeze) • Sealed from surface 15 Myr ago melting & freezing

  30. Trapped gases • Pressure 345 bars • Water supersaturated with N2 and O2 (2.5L/kg) • 50 times more than usual freshwater lake • Are these polar or apolar? A. Polar B. Apolar

  31. Trapped gases • Pressure 345 bars • Water supersaturated with N2 and O2 (2.5L/kg) • 50 times more than usual freshwater lake • Apolar don’t dissolve! • Gases can be trapped in clathrates • Cages of hydrogen-bonded frozen water molecules • Unstable when brought to surface

  32. Biology in Lake Vostok • Oligotrophic: very few nutriens • Complete darkness • Ice core drillings: • hydrogenophilusthermolutelus • But could be contamination

  33. Lake Vostok • Ice cores: age > 420,000 yr • Halted 100m above lake: to avoid contamination • Kerosene, Freon (antifreeze) • Cleaned & continued in 2012 • 94% bacteria, 6% eukaria • DNA sequencing: 255 know + 1 unknown • Contamination? • May 2013: historic monument

  34. Friday • Titan • Methane cycle (!) • RGS pp. 171 – 178, 191 – 196 • Table 5.3

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